1. Field of the Invention
This invention relates to an electronic flash unit having two capacitors of small and large capacitances for storing charges to fire a flash tube and using an electrical power source for supplying voltage to charge these capacitors in common as the drive electrical power source for another load, and a camera system using the same.
2. Description of the Related Art
In has already been known to provide an electronic flash unit in which besides the usual storage capacitor of large capacitance, there is further provided a second storage capacitor of small capacitance, too, arranged to be first charged so that even before the first capacitor of large capacitance is fully charged, as the capacitance of the second capacitor is so small that its charging is instantaneously completed, it is made possible to insure that for snap shots, a stable operation of the camera goes along, when the voltage stored on the second capacitor is used as the trigger, as disclosed in Japanese Laid-Open Patent Application No. Sho 58-97035.
Also, in recent years, what is formed by introducing into the electronic flash unit a load which is operated by the common electrical power source of these capacitors and is liable to fall in malfunctions when the voltage of the electrical power source drops below a certain level, is realized to an article of commodity. As an example of such load mention may be made of a light-emitting diode (LED) constituting part of the auto-focus device using its light as the auxiliary light. Though the above-described LED may be the generally available one, the required brilliance of the LED is considerably high. For this purpose, the current necessary to drive the LED must be increased to as high as several hundreds of milliamperes. To allow for maintaining this current flow at such an high intensity, its forward voltage should be made to lie as high as 3 volts or thereabout. As the above-described first capacitor is used in combination with a voltage booster or DC/DC converter, when the first capacitor is being charged, the battery voltage is caused to fall considerably. If an event that the command for energizing the above described LED of the AF device is given from the camera to the flash unit coincides with the charging of the first capacitor, therefore, a problem will often be encountered that the LED cannot emit as intense light as is desired.
Another example of the load is an electric motor for moving a Fresnel lens in order to alter the angular coverage of illumination of the projected flash light. To assure production of the driving torque from the motor, the voltage applied across the ends of winding of the motor must be sufficiently high. Or otherwise, a faulty operation would often result. To avoid this, therefore, similarly to the case of the LED, the time for which the motor is energized must be displaced from that for charging the first capacitor. Thus, the problem arises that the quickness of snap shots is sacrificed.